Method and system for providing closed loop color control between a scanned color image and the output of a color printer

• US 5,107,332 A
• Filed: 05/17/1989
• Issued: 04/21/1992
• Est. Priority Date: 05/17/1989
• Status: Expired due to Term

• Current Assignee: Hewlett-Packard Company (HP Inc.)
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Chan, C. S.
• Primary Examiner(s): Britton, Howard W.
• Assistant Examiner(s): Powell, Mark R.
• Application Number:
  US07/353,859
• Time in Patent Office: 1,070 Days
• Field of Search: 358/75, 358/75 IJ, 358/80
• US Class Current: 358/518
• CPC Class Codes: H04N 1/40006 Compensating for the effects of ageing, i.e. changes over time
• CPC Class Codes: H04N 1/6033 using test pattern analysis H04N1/6055 takes precedence
• CPC Class Codes: H04N 1/6036 involving periodic tests or tests during use of the machine

Abstract

A method and system for continuously correcting for errors in color output of a color copier or printer and caused by events that occur between the input of a color image scanner and the output of a copier or printer driven thereby. This method and system includes, among other things, the continuous comparison of input test pattern data, TP_in, from a small color gamut or "patch" having only a selected few number of color pixels therein with the output test pattern data, TP_out, from a color printer or copier to generate a color correction conversion factor, H. Then, H is used to continuously update an initial full scale look up table which was initially prepared from a full scale color gamut. The initial look up table has a color conversion factor, F_old, and H is used to convert F_old to F_new where F_new =H·F_old. In this manner, H continuously corrects for undesirable changes in parameters used to generate the initial look up table, such as quality of print media, ink, dye loading, ink drop volume, pen types and the calibration of system devices.

Claims

1. A method for matching the color of an image read by a color image scanner and the printed hardcopy output of a copier or printer controlled by the scanner, which comprises the steps of:

a. providing a full scale color gamut based upon preselected parameters such as print media, inks, dyes, drop volumes and pen types,

b. constructing an initial look up table based upon said full scale color gamut and storing said initial look up table in a computer,

c. comparing a sample test pattern of input information, TP_in, read by a scanner with a test pattern of output information, TP_out, generated by a color printer or color copier to in turn generate a corresponding transformation matrix, H, and

d. utilizing said transformation matrix H to continuously update said initial look up table, so that the color differences between the image scanned by said color scanner and the hardcopy output of a color printer or color copier are always driven toward zero, corrected and minimized.

2. The method defined in claim 1 wherein the continuous updating of said look up table comprises multiplying a previously generated color conversion factor, F_old, by said transformation matrix, H, to obtain an updated color conversion factor, F_new.

3. A system for continuously matching the color of an image read by a color image scanner and the printed hard copy output of a copier or printer controlled by the scanner which comprises:

a. color gamut means for providing a full scale color gamut based upon preselected parameters such as print media, inks, dyes, drop volumes and pen types,

b. means for said color gamut means for constructing an initial up table based upon said full scale color gamut and of said initial look up table in memory,

c. means for a sample test pattern of smaller color gamut information, TP_in, read by a scanner with a test pattern of output information, TP_out, generated by a color printer or color copier to thereby generate a corresponding transformation factor, H, and

d. means for utilizing said transformation matrix, H, to continuously update said initial look up table, so that the color differences between the image scanned by said color scanner and the hardcopy output of a color printer or copier are always driven towards zero, corrected and minimized.

4. The system defined in claim 3 which includes:

a. printer means responsive to data stored in said initial look up table for generating said output information, TP_out, and

b. computer means connected to said printer means for said TP_out information and further connected to said color scanner for receiving said TP_in information and for generating said transformation matrix, H, where TP_in =H·

TP_out.

5. The system defined in claim 4 wherein said computer means further includes:

a. means for continuously updating a previously generated color conversion factor, F_old, to a newly updated color conversion factor, F_new, where F_new =H·

F_old, and

b. means for applying said updated color conversion factor F_new to a color look up table for continuously updating said look up table which may be stored in memory.

6. A method for matching the color of an image read by a color image scanner and the printed hardcopy output of a copier or printer controlled by the scanner, which comprises the steps of:

a. constructing an initial look up table based upon a full scale color gamut and storing said initial look up table in a computer,

b. providing a small scale color gamut which is significantly less in size than the size of said full scale color gamut,

c. scanning said small scale color gamut to thereby generate a sample test pattern of input information, TP_in,

d. generating a test pattern of output information, TP_out, at the output of a color printer or copier to in turn generate a corresponding transformation matrix, H, in the equation TP_in =H·

TP_out, and

e. utilizing and processing said transformation matrix, H, to continuously update said initial look up table, so that the color differences between the image scanned by said color scanner and the hardcopy output of a color printer or color copier are always minimized.

7. The method defined in claim 6 wherein the continuous updating of said look up table comprises multiplying a previously generated color conversion factor, P_old, by said transformation matrix, H, to obtain an updated color conversion factor, F_new.

8. The method defined in claim 7 wherein a small scale color gamut is provided and used for the generation of TP_in and consists of a matrix of color patches having a size on the order of six rows and four columns of individual color patches, whereby to a first order approximation the computational effort to generate TP_in is proportional to N³, where N is the number of patches in said small scale color gamut.

9. A system for matching the color of an image read by a color image scanner and the printed hardcopy output of a copier or printer controlled by the scanner including, in combination:

a. means including an initial look up table based upon a full scale color gamut and means for storing said initial look up table in a computer,

b. means for providing a small scale color gamut which is significantly less in size than said full scale color gamut,

c. means for scanning said small scale color gamut and thereby generating a sample test pattern of input information, TP_in,

d. means connected to said computer for providing a test pattern of output information, TP_out, and generated by a color printer or copier to in turn generate a corresponding transformation matrix, H, where H is defined by the equation TP_in =H·

TP_out, and

e. means connected to said color printer and operable to receive said transformation matrix, H, and being further operative to continuously update said initial look up table, so that the color differences between the scanned image read by said color scanner and the hardcopy output of a color printer or color copier are always minimized.

10. The system defined in claim 9 which further includes color conversion means connected to said transformation matrix generating means for continuously updating said look up table by multiplying a previously generated color conversion factor, F_old, by said transformation matrix, H, to obtain an updated color conversion factor, F_new.

11. The system defined in claim 10 wherein a small scale color gamut is provided and used in the generation of TP_in and consists of a matrix of color patches having a size on the order of six rows and four columns of individual color patches, whereby to a first order approximation the computational effort to generate TP_in proportional to N³, where N is the number of patches in said small scale color gamut.